1. Field of the Invention
The present invention relates to a focusing optical system in which light is emitted from plural light sources in accordance with image information and which focuses light.
2. Description of the Related Art
Currently, there are image exposing devices in which plural light sources, which are disposed in a matrix-like arrangement at a predetermined position of the device, and a photosensitive material are moved relatively in a main scanning direction and a subscanning direction such that the photosensitive material is exposed. The light from the plural light sources is focused onto the photosensitive material by a focusing optical system. For example, semiconductor elements such as LEDs are used as the light sources, and these semiconductor elements are arranged in a matrix-like arrangement at a predetermined pitch.
However, in actuality, there are cases in which the light sources are not disposed at a predetermined pitch. Namely, there are cases in which positional offset (so-called pitch offset) occurs between the desired arrangement of positions of the light sources and the actual arrangement of positions. Due to this pitch offset, the distribution of the amount of light at the time of scanning the light sources and the photosensitive material relatively may be uneven and the image quality may deteriorate.
In order to reduce the unevenness in the distribution of the amount of light due to pitch offset, for example, reducing the focusing magnification of the lens forming the focusing optical system has been considered. Namely, by reducing the focusing magnification, the absolute amount of the pitch offset on the photosensitive material is reduced. However, if the focusing magnification of the lens is reduced, the spot size on the photosensitive material is also reduced, and even if the absolute amount of the pitch offset is low, the unevenness in the distribution of the amount of light will be great.